article that goes in depth about Raptor development and the use of a spark igniter.

The diagram which has been posted in various places, is very clear on the continuous running mode, assuming that the preheated CH4 is going to mix, prebuurn and and burn properly with the cold LOX. This motor has got to run after sitting months on Mars

What seems to be missing is the initial 'cold start" spinup mode. Can anyone suggest some options ? Here are a few to start with:

1. an electric starter motor as on cars and the Electron rocket ?
2. a cylinder of warmed gaseous oxygen and another of warmed gaseous methane to spin up the respective turbines
3. a specific starter turbine on the same shaft which is spun up with pre-warmed gaseous nitrogen ?
   

Don't we also need a spark ignition system in three cases: for the two preburners and the combustion chamber. Spark-igniting the preburners could be the hardest since the gases are cold and the mixture isn't optimal for either.